The Black Friday holiday sales weekend is always a stressful time for brands as they scramble to hit the right balance between ad spend and profitable sales. Yet this past weekend was even more stressful than usual when a key reporting metric from Amazon’s Ad console began doling out erroneous information.

The issues started late Friday afternoon, according to Ryan Walker, VP of operations at Momentum Commerce, a digital retail consultancy that manages Amazon advertising for 20 brands.

Amazon provides a dashboard that keeps track of ad spend, including sponsored products, sponsored brands and sponsored display ads, for each brand. Companies use this report and their own sales data to decide how best to allocate their ad budgets.

By Friday evening, the ad spends reported by Amazon were roughly 50% less than brands expected them to be. Consumers could still see the sponsored ads, but on the back end, brands had no idea how much they had spent thus far on advertising.

“The brand relies on Amazon’s reported numbers to know how much they had spent today relative to what they planned,” said Walker, who has worked with brands on their Black Friday campaigns for Amazon for several years but has never seen an outage like this before. “We mostly relied on the sales numbers to make decisions,” he said. “But we were completely blind as to what we were going to end up spending.”

“We identified a reporting delay for some sponsored ads metrics over the weekend. This is resolved and reporting is now current. We will work with our advertisers to ensure they have the best possible experience with all Amazon Ads products," said an Amazon spokeswoman.

Over the weekend, some brands trying to see their ad spend metrics saw an error message instead. The message was shared with Ad Age by a consultant.

“We are investigating an issue in reporting of sponsored ads performance metrics. No data has been lost, and any missing information will be available after the issue is resolved. Ad delivery is not affected by this issue. We are actively working to fix this issue as soon as possible. We apologize for the inconvenience," the message read. 

Meanwhile, early sales reports from the holiday weekend showed strong consumer spending online. E-commerce sales were up 2.3% over last year to $9.12 billion on Black Friday and up 4.4% over last year to $9.55 billion over Saturday and Sunday, according to data from Adobe Analytics.

The damage from Amazon’s incorrect reports for a brand could be long-lasting, especially if that brand banked on a big campaign over the crucial holiday weekend, experts said.

“There will be brands that overspent by accident—that would mean they won’t have as much to spend the rest of the year on ads if they have a fixed budget,” said Kiri Masters, head of retail marketplace strategy at ad agency Acadia. Conversely, “if they’ve underspent, then they’ve lost this golden opportunity to capture shoppers at an important time of the year that they might not be able to make up before the end of the year,” she added.

One brand executive, who spoke on the condition of anonymity, said he plans to talk to Amazon about the situation “once the dust settles” to see “what can be done to prevent this from happening again in the future and how they can improve their communication timeliness and content as well.”